Method for improving the performance of a dehydrogenation catalyst

Abstract

The present development relates to a modification of the Houdry process for the dehydrogenation of aliphatic hydrocarbons, whereby the dehydrogenation cycle is extended, or lengthened, and hydrogen gas is added into the reaction. The combination of the extended cycle with the hydrogen introduction results in a surprising stabilization of the production rate in the dehydrogenation process. The hydrogen gas may be introduced through a recycle step. The process of the present development is demonstrated for the dehydrogenation of propane to propylene.

1. In a standard Houdry process for the dehydrogenation of aliphatic hydrocarbons wherein the process defines a cycle that includes the stages of:
 (a) loading a dehydrogenation catalyst into a reactor to form a catalyst bed wherein the bed defines a top section, a middle section and a bottom section; 
 (b) evacuating the catalyst bed; 
 (c) reducing the catalyst bed with hydrogen and evacuating the bed; 
 (d) introducing an aliphatic hydrocarbon into the catalyst bed as a gas feed at a preselected flow rate and such that the feed initially contacts the top section of the bed and exits after contact with the bottom section and after the hydrocarbon is dehydrogenated; 
 (e) steam purging and regenerating the catalyst bed; 
 (f) repeating stages (b) through (e); and 
 
       wherein the length of stages (b) through (e) are controlled by a sequencer, the improvement of
 (1) extending the cycle length by the introduction of a delay of at least one predetermined time interval into at least one stage of the cycle; and 
 (2) introducing hydrogen gas, at concentration of up to about 7 mol % H 2 , into the reaction at stage (d). 
 
     
     
       2. The process of  claim 1  wherein the reaction cycle is extended by the introduction of one or more delays added to a program controlling the sequencer. 
     
     
       3. The process of  claim 2  wherein the delay is defined in terms of minutes. 
     
     
       4. The process of  claim 2  wherein the delay is defined in terms of seconds. 
     
     
       5. The process of  claim 1  wherein the extended reaction cycle produces temperature ranges in each section of the catalyst bed that are greater than the temperature ranges produced in a standard Houdry process. 
     
     
       6. The process of  claim 1  wherein the hydrogen gas added at stage (d) is added at concentrations of from about 2 mol % H 2  to about 7 mol % H 2 . 
     
     
       7. The process of  claim 1  wherein the hydrogen gas source for introduction at stage (d) is from a recycle process associated with the dehydrogenation reaction. 
     
     
       8. The process of  claim 1  wherein a plurality of reactors function in tandem in a manner such that while a first set of reactors is receiving feed (stage d), a second set of reactors is in the regeneration stage (stage e), and wherein the delay introduced in the first set of reactors results in a concomitant delay in the second set of reactors. 
     
     
       9. The process of  claim 8  wherein the length of the process stages for each set of reactors is controlled from the sequencer. 
     
     
       10. The process of  claim 8  wherein a modification in the length of any process stage in the first set of reactors is accompanied by an essentially equal modification in the length of the same process stage for the second set of reactors. 
     
     
       11. In a standard Houdry process for the dehydrogenation of aliphatic hydrocarbons wherein the process defines a cycle that includes the stages of:
 (a) loading a dehydrogenation catalyst into a reactor to form a catalyst bed wherein the bed defines a top section, a middle section and a bottom section; 
 (b) evacuating the catalyst bed; 
 (c) reducing the catalyst bed with hydrogen and evacuating the bed; 
 (d) introducing an aliphatic hydrocarbon into the catalyst bed as a gas feed at a preselected flow rate and such that the feed initially contacts the top section of the bed and exits after contact with the bottom section and after the hydrocarbon is dehydrogenated; 
 (e) steam purging and regenerating the catalyst bed; 
 (f) repeating stages (b) through (e); and 
 
       wherein a plurality of reactors function in tandem in a manner such that while a first set of reactors is receiving feed (stage d), a second set of reactors is in the regeneration stage (stage e), and the length of stages (b) through (e) are controlled by a sequencer, the improvement of
 (1) extending the length of at least one stage of the cycle for each set of reactors by the introduction of one or more delays of a predetermined time interval added to a program controlling the sequencer; and 
 (2) introducing hydrogen gas into the reaction at stage (d) at concentrations of up to about 7 mol % H 2 . 
 
     
     
       12. The process of  claim 11  wherein the hydrogen gas added at stage (d) is added at concentrations of from about 2 mol % H 2  to about 7 mol % H 2 . 
     
     
       13. The process of  claim 11  wherein the hydrogen gas source for introduction at stage (d) is from a recycle process associated with the dehydrogenation reaction. 
     
     
       14. The process of  claim 11  wherein the length of the cycle for each set of reactors is controlled from the sequencer. 
     
     
       15. The process of  claim 14  wherein the delay introduced in the first set of reactors results in a concomitant delay in the second set of reactors.